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Getting value from json item in java

I have a json file, for example:
{
"A":"-0.4",
"B":"-0.2",
"C":"-0.2",
"D":"X",
"E":"0.2",
"F":"0.2",
"J":"0.3"
}
I want return each element of a list json when I call it via my function.
I did a function to do this:
public JSONObject my_function() {
JSONParser parser = new JSONParser();
List<JSONObject> records = new ArrayList<JSONObject>();
try (FileReader reader = new FileReader("File.json")) {
//Read JSON file
Object obj = parser.parse(reader);
JSONObject docs = (JSONObject) obj;
LOGGER.info("read elements" + docs); // it display all a list of a json file like this: {"A":"-0.4","B":"-0.2","C":"-0.2","D":"X","E":"0.2","F":"0.2","J":"0.3"}
for (int i = 0; i < docs.size(); i++) {
records.add((JSONObject) docs.get(i));
System.out.println((records)); // it return null
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ParseException e) {
e.printStackTrace();
}
LOGGER.info("The first element of a list is:" +records.get(0)); // return null
return records.get(0);
How can I change my function to return the value of each element in a json file.
For example, when I call my_function:
my_function.get("A") should display -0.4
Thank you

First you need a Class for mapping
public class Json {
private String a;
private String b;
private String c;
private String d;
private String e;
private String f;
private String j;
//getters and setters
}
Then in your working class
ObjectMapper mapper = new ObjectMapper();
//JSON from file to Object
Json jsn = mapper.readValue(new File("File.json"), Json.class);
then you can use that object in a usual way...
here is the dependency I used
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.6.3</version>
</dependency>
Reference

In Java you can use only class`s methods, as I know.
If you want to get your second element by its first, you should in your class create 2 methods like
class Main {
Map<String, String> records = new HashMap<>();
public JSONObject my_function() {
// your realization where you should insert your pairs into Map.
}
public String get(String firstElement){
return map.getValue(firstElement);
}
}
class someOtherClass {
Main main = new Main();
main .my_function();
main .get("A");
}

Parsing JsonObjectRequest

I am new to Android and JAVA and I am trying to parse a json response. I know how to parse jsonarray but no Idea how to parse jsonobject. Can someone tell me how? Below is my Response.
{"118":{"garment_color":"Blue","garment_name":"skjhkds","garment_price":"232"},"119":{"garment_color":"hjsadjjs","garment_name":"sdasd","garment_price":"23478"}}
And this is how parsed jsonarray.
public void JSON_DATA_WEB_CALL(){
jsonArrayRequest = new JsonArrayRequest(GET_JSON_DATA_HTTP_URL,
new Response.Listener<JSONArray>() {
#Override
public void onResponse(JSONArray response) {
progressBar.setVisibility(View.INVISIBLE);
JSON_PARSE_DATA_AFTER_WEBCALL(response);
}
},
new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
}
});
requestQueue = Volley.newRequestQueue(this);
requestQueue.add(jsonArrayRequest);
}
public void JSON_PARSE_DATA_AFTER_WEBCALL(JSONArray array){
for(int i = 0; i<array.length(); i++) {
GetDataAdapter GetDataAdapter2 = new GetDataAdapter();
JSONObject json = null;
try {
json = array.getJSONObject(i);
GetDataAdapter2.setImageTitleNamee(json.getString(JSON_IMAGE_TITLE_NAME));
//GetDataAdapter2.setImageServerLarger(json.getString(JSON_IMAGE_LARGER));
GetDataAdapter2.setImageServerUrl(json.getString(JSON_IMAGE_URL));
GetDataAdapter2.setMrp_price(json.getString(JSON_MRP_PRICE));
GetDataAdapter2.setDisc_price(json.getString(JSON_DISC_PRICE));
} catch (JSONException e) {
e.printStackTrace();
}
GetDataAdapter1.add(GetDataAdapter2);
}
recyclerViewadapter = new RecyclerViewAdapter(GetDataAdapter1, this);
recyclerView.setAdapter(recyclerViewadapter);
}
Please Someone help. Thanks.

In my opinion, use Gson library, where you give it the json object/array/string and it automatically parses it into a java object. Note that you have to define the java class with the appropriate fields.
EDIT: So here's an answer that goes with the suggested guidelines:
First create your model classes just like you will receive them from the server:
public class MyServerObject {
MyGarment jsonKeyName;
}
public class MyGarment {
String garment_color;
String garment_name;
String garment_price;
}
Next, after receiving your json string, parse it using Gson:
Gson gson = new Gson();
String json= "{"jsonKeyName":{"garment_color":"Blue","garment_name":"skjhkds","garment_price":"232"};
MyServerObject serverObject = gson.fromJson(json, MyServerObject.class);
Now, you can access your Garment object from your server object with all the values parsed correctly. Also note that if you're receiving a json array you could add the object as a list in your MyServerObject.class.
Hope this helps.

as per my above comment
you need to make JSONObject request instead of JSONArray request
try this to parse your JSON Response
try {
JSONObject jsonObject= new JSONObject("Response");
JSONObject jsonObject1=jsonObject.getJSONObject("118");
String garment_color=jsonObject1.getString("garment_color");
String garment_name=jsonObject1.getString("garment_name");
String garment_price=jsonObject1.getString("garment_price");
JSONObject jsonObject2=jsonObject.getJSONObject("119");
String garment_color2=jsonObject1.getString("garment_color");
String garment_name2=jsonObject1.getString("garment_name");
String garment_price2=jsonObject1.getString("garment_price");
} catch (JSONException e) {
e.printStackTrace();
}

Use StringRequest instead of JSONObject/JSONArray request and finally fetch value like this:
JSONObject object = new JSONObject(YOUR JSON RESPONSE);
String s1 = object.getJSONObject("118").getString("garment_color");

Get Class Type of Object and use it in a Variable Declaration

What I am trying to do, and I don't know whether this is possible, is to get the class type of an object, and then use it in a declaration. I am using the Gson library for Json Conversion and I want to create a method that can take any object Arraylist type and convert it into a JsonArray. What I have below is code. Arraylist of type X will are casted down to type Object and than passed to the method below. The INSERT_CLASS_HERE should be dynamic based on the Object type.
public static JsonArray getJsonArray(List<Object> list , Class theClass){
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(list, new TypeToken<List<INSERT_CLASS_TYPE_HERE>>() {}.getType());
if (! element.isJsonArray()) {
try {
throw new Exception();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
JsonArray jsonArray = element.getAsJsonArray();
return jsonArray;
}
What I tried was the following but this isn't correct syntax and will throw errors
public static JsonArray getJsonArray(List<Object> list , Class theClass){
if(list.size() == 0) return null;
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(list, new TypeToken<List<theClass>>() {}.getType());
if (! element.isJsonArray()) {
// fail appropriately
try {
throw new Exception();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
JsonArray jsonArray = element.getAsJsonArray();
return jsonArray;
}
1) Is this possible to do, and if not why not?
2) If it is not, how can this be achieved?
Thank you!

Why are you passing in a type value? That should not be required.
public static JsonArray getJsonArray(List<Object> list){
if(list.size() == 0) return null;
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(list);
JsonArray jsonArray = element.getAsJsonArray();
return jsonArray;
}
Better yet to avoid casting you can do the following
public static <T> JsonArray getJsonArray(List<T> list){
if(list.size() == 0) return null;
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(list);
JsonArray jsonArray = element.getAsJsonArray();
return jsonArray;
}

It seems what you are trying to do is along the lines of Java generics.
This should be fairly simply to do using generics:
public static <T> JsonArray getJsonArray(List<T> list){
if(list.size() == 0) return null;
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(list, new TypeToken<List<T>>() {}.getType());
//Not familiar with gson, but you might be able to just use T here instead

Try modifying your method signature like this:
public static <T> JsonArray getJsonArray(List<Object> list, Class<T> theClass )
You should then be able to do this:
new TypeToken<List<T>>

Faster way to parse a JSON String in android

I'm using this method to parse a JSON string, but it is too slow... is there a better way to do it?
Thanks
synchronized private void parseCategories(String response){
try{
JSONArray categoriesJSONArray = new JSONArray (response);
// looping through All Contacts
for(int i = 0; i < categoriesJSONArray.length(); i++){
JSONObject currentCategory = categoriesJSONArray.getJSONObject(i);
String label="";
String categoryId="";
// Storing each json item in variable
if(currentCategory.has("label"))
label = currentCategory.getString("label");
if(currentCategory.has("id"))
categoryId = currentCategory.getString("id");
if(
label!=null &&
categoryId!=null
)
{
Category toAdd = new Category(categoryId, label);
categories.add(toAdd);
}
}
//Alphabetic order
Collections.sort(
categories,
new Comparator<Feed>() {
public int compare(Feed lhs, Feed rhs) {
return lhs.getTitle().compareTo(rhs.getTitle());
}
}
);
Intent intent = new Intent("CategoriesLoaded");
LocalBroadcastManager.getInstance(mAppContext).sendBroadcast(intent);
}catch (JSONException e) {
e.printStackTrace();
}
}

Here's try following code to start with. You would need Gson library for it.
Gson gson=new Gson();
MyBean myBean=gson.fromJson(response);
Note: Here MyBean class contains the fields present in you json string for e.g. id, along with getter and setters. Rest of all is handled by Gson.
Here's a quick demo.
import com.google.gson.annotations.SerializedName;
public class Box {
#SerializedName("id")
private String categoryId;
// getter and setter
}
Say you JSON looks as following:
{"id":"A12"}
You can parse it as follows:
class Parse{
public void parseJson(String response){
Gson gson=new Gson();
Box box=gson.fromJson(response,Box.class);
System.out.println(box.getCategoryId());
}
}
Output :
A12
For more on Gson visit here

Use GSON library. You can convert your object to json string like the following example:
MyClass MyObject;
Gson gson = new Gson();
String strJson = gson.toJson(MyObject);

How to convert list data into json in java

I have a function which is returning Data as List in java class. Now as per my need, I have to convert it into Json Format.
Below is my function code snippet:
public static List<Product> getCartList() {
List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
for(Product p : cartMap.keySet()) {
cartList.add(p);
}
return cartList;
}
I tried To convert into json by using this code but it is giving type mismatch error as function is of type List...
public static List<Product> getCartList() {
List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
for(Product p : cartMap.keySet()) {
cartList.add(p);
}
Gson gson = new Gson();
// convert your list to json
String jsonCartList = gson.toJson(cartList);
// print your generated json
System.out.println("jsonCartList: " + jsonCartList);
return jsonCartList;
}
Please help me resolve this.

Using gson it is much simpler. Use following code snippet:
// create a new Gson instance
Gson gson = new Gson();
// convert your list to json
String jsonCartList = gson.toJson(cartList);
// print your generated json
System.out.println("jsonCartList: " + jsonCartList);
Converting back from JSON string to your Java object
// Converts JSON string into a List of Product object
Type type = new TypeToken<List<Product>>(){}.getType();
List<Product> prodList = gson.fromJson(jsonCartList, type);
// print your List<Product>
System.out.println("prodList: " + prodList);

public static List<Product> getCartList() {
JSONObject responseDetailsJson = new JSONObject();
JSONArray jsonArray = new JSONArray();
List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
for(Product p : cartMap.keySet()) {
cartList.add(p);
JSONObject formDetailsJson = new JSONObject();
formDetailsJson.put("id", "1");
formDetailsJson.put("name", "name1");
jsonArray.add(formDetailsJson);
}
responseDetailsJson.put("forms", jsonArray);//Here you can see the data in json format
return cartList;
}
you can get the data in the following form
{
"forms": [
{ "id": "1", "name": "name1" },
{ "id": "2", "name": "name2" }
]
}

Try these simple steps:
ObjectMapper mapper = new ObjectMapper();
String newJsonData = mapper.writeValueAsString(cartList);
return newJsonData;
ObjectMapper() is com.fasterxml.jackson.databind.ObjectMapper.ObjectMapper();

i wrote my own function to return list of object for populate combo box :
public static String getJSONList(java.util.List<Object> list,String kelas,String name, String label) {
try {
Object[] args={};
Class cl = Class.forName(kelas);
Method getName = cl.getMethod(name, null);
Method getLabel = cl.getMethod(label, null);
String json="[";
for (int i = 0; i < list.size(); i++) {
Object o = list.get(i);
if(i>0){
json+=",";
}
json+="{\"label\":\""+getLabel.invoke(o,args)+"\",\"name\":\""+getName.invoke(o,args)+"\"}";
//System.out.println("Object = " + i+" -> "+o.getNumber());
}
json+="]";
return json;
} catch (ClassNotFoundException ex) {
Logger.getLogger(JSONHelper.class.getName()).log(Level.SEVERE, null, ex);
} catch (Exception ex) {
System.out.println("Error in get JSON List");
ex.printStackTrace();
}
return "";
}
and call it from anywhere like :
String toreturn=JSONHelper.getJSONList(list, "com.bean.Contact", "getContactID", "getNumber");

Try like below with Gson Library.
Earlier Conversion List format were:
[Product [Id=1, City=Bengalore, Category=TV, Brand=Samsung, Name=Samsung LED, Type=LED, Size=32 inches, Price=33500.5, Stock=17.0], Product [Id=2, City=Bengalore, Category=TV, Brand=Samsung, Name=Samsung LED, Type=LED, Size=42 inches, Price=41850.0, Stock=9.0]]
and here the conversion source begins.
//** Note I have created the method toString() in Product class.
//Creating and initializing a java.util.List of Product objects
List<Product> productList = (List<Product>)productRepository.findAll();
//Creating a blank List of Gson library JsonObject
List<JsonObject> entities = new ArrayList<JsonObject>();
//Simply printing productList size
System.out.println("Size of productList is : " + productList.size());
//Creating a Iterator for productList
Iterator<Product> iterator = productList.iterator();
//Run while loop till Product Object exists.
while(iterator.hasNext()){
//Creating a fresh Gson Object
Gson gs = new Gson();
//Converting our Product Object to JsonElement
//Object by passing the Product Object String value (iterator.next())
JsonElement element = gs.fromJson (gs.toJson(iterator.next()), JsonElement.class);
//Creating JsonObject from JsonElement
JsonObject jsonObject = element.getAsJsonObject();
//Collecting the JsonObject to List
entities.add(jsonObject);
}
//Do what you want to do with Array of JsonObject
System.out.println(entities);
Converted Json Result is :
[{"Id":1,"City":"Bengalore","Category":"TV","Brand":"Samsung","Name":"Samsung LED","Type":"LED","Size":"32 inches","Price":33500.5,"Stock":17.0}, {"Id":2,"City":"Bengalore","Category":"TV","Brand":"Samsung","Name":"Samsung LED","Type":"LED","Size":"42 inches","Price":41850.0,"Stock":9.0}]
Hope this would help many guys!

JSONObject responseDetailsJson = new JSONObject();
JSONArray jsonArray = new JSONArray();
List<String> ls =new ArrayList<String>();
for(product cj:cities.getList()) {
ls.add(cj);
JSONObject formDetailsJson = new JSONObject();
formDetailsJson.put("id", cj.id);
formDetailsJson.put("name", cj.name);
jsonArray.put(formDetailsJson);
}
responseDetailsJson.put("Cities", jsonArray);
return responseDetailsJson;

You can use the following method which uses Jackson library
public static <T> List<T> convertToList(String jsonString, Class<T> target) {
if(StringUtils.isEmpty(jsonString)) return List.of();
return new ObjectMapper().readValue(jsonString, new ObjectMapper().getTypeFactory().
constructCollectionType(List.class, target));
} catch ( JsonProcessingException | JSONException e) {
e.printStackTrace();
return List.of();
}
}

if response is of type List , res.toString() is simply enough to convert to json or else we need to use
ObjectMapper mapper = new ObjectMapper();
String jsonRes = mapper.writeValueAsString(res);